Textbook Question
Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (a) What is the enthalpy change for the reverse reaction?
Ch.5 - Thermochemistry
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement177
- Ch.2 - Atoms, Molecules, and Ions231
- Ch.3 - Chemical Reactions and Reaction Stoichiometry216
- Ch.4 - Reactions in Aqueous Solution189
- Ch.5 - Thermochemistry175
- Ch.6 - Electronic Structure of Atoms168
- Ch.7 - Periodic Properties of the Elements150
- Ch.8 - Basic Concepts of Chemical Bonding177
- Ch.9 - Molecular Geometry and Bonding Theories200
- Ch.10 - Gases179
- Ch.11 - Liquids and Intermolecular Forces113
- Ch.12 - Solids and Modern Materials154
- Ch.13 - Properties of Solutions157
- Ch.14 - Chemical Kinetics199
- Ch.15 - Chemical Equilibrium128
- Ch.16 - Acid-Base Equilibria164
- Ch.17 - Additional Aspects of Aqueous Equilibria163
- Ch.18 - Chemistry of the Environment105
- Ch.19 - Chemical Thermodynamics164
- Ch.20 - Electrochemistry171
- Ch.21 - Nuclear Chemistry122
- Ch.22 - Chemistry of the Nonmetals82
- Ch.23 - Transition Metals and Coordination Chemistry79
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry16
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
Chapter 5, Problem 48c
Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (c) Which is more likely to be thermodynamically favored, the forward reaction or the reverse reaction?
Verified step by step guidance1
Identify the sign of the enthalpy change (ΔH) for the reaction. A positive ΔH indicates that the reaction is endothermic, meaning it absorbs heat from the surroundings.
Understand that thermodynamically favored reactions are generally those that release energy (exothermic reactions), where ΔH is negative, as they lead to a decrease in the system's enthalpy, making the products more stable than the reactants.
Compare the enthalpy change of the forward reaction, which is +630 kJ, indicating that it is endothermic and requires energy input to proceed.
Consider the reverse reaction, where the sign of ΔH would be negative (-630 kJ), suggesting that it is exothermic. This reaction would release energy, making it more likely to occur spontaneously under standard conditions.
Conclude that the reverse reaction, forming liquid benzene from gaseous acetylene, is more likely to be thermodynamically favored due to its exothermic nature.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Thermodynamics and Reaction Favorability
Thermodynamics is the study of energy transformations, particularly how energy changes influence the direction of chemical reactions. A reaction is thermodynamically favored if it leads to a decrease in free energy, typically indicated by a negative change in Gibbs free energy (ΔG). In this context, the forward reaction's positive enthalpy change (ΔH = +630 kJ) suggests it absorbs heat, which may affect its favorability.
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First Law of Thermodynamics
Enthalpy and Reaction Energy
Enthalpy (H) is a measure of the total energy of a thermodynamic system, including internal energy and the energy required to make room for it by displacing its environment. A positive ΔH indicates that the reaction is endothermic, meaning it requires energy input. Understanding the enthalpy change helps predict whether a reaction will proceed spontaneously under given conditions.
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Entropy and Disorder
Entropy (S) is a measure of the disorder or randomness in a system. In chemical reactions, an increase in the number of gas molecules typically leads to an increase in entropy, which can favor the reaction despite a positive enthalpy change. In this case, the decomposition of liquid benzene into gaseous acetylene increases the number of gas molecules, potentially making the forward reaction more favorable from an entropy perspective.
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Related Practice
Textbook Question
Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (b) What is H for the formation of 1 mol of acetylene?
Textbook Question
Consider the combustion of liquid methanol, CH3OH(l): CH3OH(l) + 3/2 O2(g) → CO2(g) + 2 H2O(l) ΔH = -726.5 kJ (d) If the reaction were written to produce H2O(g) instead of H2O(l), would you expect the magnitude of ΔH to increase, decrease, or stay the same? Explain.
Textbook Question
(b) The specific heat of aluminum is 0.9 J/(g - K). Calculate its molar heat capacity.
Textbook Question
Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (d) If C6H6(g) were consumed instead of C6H6(l), would you expect the magnitude of ΔH to increase, decrease, or stay the same? Explain.